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Our study provides a fresh perspective on the possible employment of SARS-CoV-2 LFA antibody tests. We developed an in-depth, large-scale analysis comparing LFA performance to enzyme-linked immunosorbent assay (ELISA) and electrochemiluminescence immunoassay (ECLIA) and evaluating their sensitivity and specificity in identifying COVID-19 patients at different time points from symptom onset.
The possibility to rely on rapid and accurate diagnostic techniques has proved itself crucial during the past year to contain the spread of SARS-CoV-2 infection [1]. Even if quantitative RT-PCR (RT-qPCR) on nasopharyngeal swab (NPS) is still considered the standard for coronavirus disease 2019 (COVID-19) diagnosis, saliva has been evaluated in several studies as a possible alternative to NPS and is currently extensively utilised in South Korea, Germany and Japan [2, 3]. Nonetheless, the use of saliva is still debated, and a rigorous standardisation of the analysis protocol is greatly needed [4–6]. The application of point-of-care technologies on saliva, able to rapidly perform highly specific and sensitive molecular testing, could prove invaluable to allow the diagnosis also in challenging and remote settings by simplifying and speeding up the diagnostic process [1].
Background: During the last year, mass screening campaigns have been carried out to identify immunological response to SARS-CoV-2 and establish a possible seroprevalence. The obtained results gained new importance with the beginning of SARS-CoV-2 vaccination campaign, as the lack of doses has persuaded several countries to introduce different policies for individuals who had a history of COVID 19. LFAs may represent an affordable tool to support population screening in LMICs, where diagnostic tests are lacking, and epidemiology is still widely unknown. However, LFAs have demonstrated a wide range of performance and the question of which one could be more valuable in these settings still remains. Methods: We evaluated the performance of 11 LFAs in detecting SARS-CoV-2 infection, analysing samples collected from 350 subjects. In addition, samples from 57 health care workers collected at 21-24 days after the first dose of Pfizer-BioNTech vaccine were also evaluated. Findings: LFAs demonstrated a wide range of specificity (92.31% to 100%) and sensitivity (50 to 100%). The analysis of serum samples post vaccination was used to describe the most suitable tests to detect IgG response against S protein RBD. History of TB therapy was identified as a potential factor affecting the specificity of LFAs. Conclusions: This analysis identified which LFAs represent a valuable tool not only for the detection of prior SARS-CoV-2 infection, but also to detect IgG elicited in response to vaccination. These results demonstrated that different LFAs may have different applications and the possible risks of their use in high TB burden settings.
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